This invention relates to an apparatus and method for marking the cornea prior to corneal surgery. More particularly, this invention relates to an apparatus and method for maintaining a patient's visual fixation and centration while marking the cornea.
Most refractive or corneal surgical procedures require proper centering on the cornea, since eccentricity of the refractive procedure may result in less than optimum visual function. To achieve the best surgical results, it is important that the corneal surgical procedure to be employed is properly centered.
Methods of marking the "center" of the cornea generally require the patient to fixate on a light or spot located on the operating microscope. Most methods use the corneal light reflex as a reference point for the surgeon to mark the cornea using an operating microscope. For example, currently used methods for centering corneal surgical procedures with an operating microscope are discussed in Uozato, U. and Guyton, D. L., "Centering Corneal Surgical Procedures," Am. J. of Ophthalmology, Vol. 103, pp. 264-75 (1987). A comparison of the use of the reflection of the operating microscope filament on the cornea surface and the use of Osher's centering device mounted on the microscope and employing a fiber optic light source is described by Steinberg, E. B. and Waring, G. O., "Comparison of Two Methods of Marking the Visual Axis on the Cornea during Radial Keratotomy," Am. J. of Ophthalmology, Vol. 96, pp. 605-08 (1983). A binocular method of aligning the eye on the visual axis for marking the center of the visual axis on the cornea using a binocular microscope is described, for example, in Sanders, D. R. et.al. (eds.), Refractive Corneal Surgery, pp. 134-35 (1986).
The apparatus and method of this invention are advantageous in that they do not necessarily require an operating microscope or any attachments affixed to the microscope to achieve accurate centering. In addition, the method and apparatus of this invention may be used for centering the cornea with greater speed and less manipulation by the surgeon.
A source of error common to all of the known methods of corneal marking is the surgeon. However, this source of error is reduced in the apparatus and method of this invention, as both are less dependent upon the alignment technique or judgment of the surgeon. This reduction of the surgeon's potential error results in the cornea being marked more accurately.
Another source of error in the known methods is due to a parallax phenomenon. This occurs when using either the corneal light reflex or the pupil for centering. However, the apparatus and method of this invention mark the cornea directly, thus eliminating this parallax error.
This invention is also advantageous in that it achieves greater accuracy over currently practiced corneal marking methods in cases where there has been extensive corneal disease since it is less dependent on a clear cornea than other methods.